1. Field of the Invention
The present invention relates to a method for driving a plasma display panel.
2. Description of the Related Art
Currently, an AC (discharge)-type plasma display panel (PDP) is commercially available as a thin display device. In a PDP, two substrates (i.e., a front transparent substrate and a rear substrate) are disposed opposite each other with a predetermined interval therebetween. Pairs of row electrodes extending in a horizontal direction of the screen are formed on an inner surface of the front transparent substrate as a display surface. The inner surface of the front transparent substrate faces the rear substrate. A dielectric layer is formed on the inner surface of the front transparent substrate such that the dielectric layer covers the pairs of row electrodes. Column electrodes extending in a vertical direction of the screen are formed on the rear substrate such that the column electrodes cross the pairs of row electrodes. When viewed from the front (i.e., from the display surface side), discharge cells, which serve as pixels, are formed at intersections of the row electrode pairs and the column electrodes.
Grayscale driving is performed on such a PDP using a subfield scheme to achieve halftone display luminance faithful to an input image signal.
In such a grayscale drive method based on the subfield scheme, each field (unit display period) is divided into a plurality of subfields and a certain number of times (or a period during which) light emission is to be performed is allocated to each subfield. Display driving of an image signal for one field is performed on the subfield basis. An addressing process and a sustain process are sequentially performed in each subfield. In the addressing process, an addressing discharge is selectively generated between a row electrode and a column electrode in each discharge cell on the basis of an input image signal. A certain amount of wall charges are generated (or erased) in those discharge cells in which the addressing discharge has been generated. In other discharge cells in which no addressing discharge has been generated, the state of wall charges is maintained unchanged from the immediately previous state. Discharge cells having a specific amount of wall charges are set to an emission mode and other discharge cells having no specific amount of wall charges are set to a non-emission mode. In the sustain process, a discharge is repeatedly generated a number of times corresponding to a luminance weight value allocated to the subfield in those discharge cells that are in the emission mode, thereby maintaining light emission through the discharge. In the first subfield, an initialization process is performed prior to the addressing process. In the initialization process, a reset pulse is simultaneously applied to every discharge cell, thereby causing a reset discharge between row electrodes in every discharge cell. This initializes the amount of wall charges remaining in every discharge cell.
Since the reset discharge is a relatively strong discharge and contributes nothing to the contents of an image to be displayed, light emission caused by this discharge leads to a reduction in image contrast, especially a reduction in dark contrast when an entirely dark image is displayed.
In one suggested drive method, the dark contrast is increased by decreasing the peak potential of the reset pulse to weaken the reset discharge as the darkness of an image to be displayed increases (i.e., as the number of those discharge cells that are in a non-emission mode in one screen increases). See FIG. 8 of Japanese Patent Application Kokai (Publication) No. 2006-243002.
However, reducing the peak potential of the reset pulse may lead to generation of an insufficient amount of wall charges due to weakening of the reset discharge. In this case, erroneous discharges occur in the subsequent sustain process.